Full disclosure: I am founder and CEO of PHP Fog
Joe hit it right on the nail here. We examined our costs very carefully and found some room to give back to our community.
The right blend that we were going for was give enough to do dev/test for free, and be reasonably priced (https://phpfog.com/pricing) when you are ready for production.
When Linode gives away more RAM or AWS makes inbound traffic free, it is not a sign these companies are less trustworthy, but that they love their users. We love developers and are trying to do right by them.